1. Field of the Invention
The present invention relates to a storage apparatus, a control method, a control device, and a program for reading/writing data by flying a head above a rotating recording medium, and particularly relates to a storage apparatus, a control method, a control device, and a program for controlling a flying height between a head and a recording medium to a predetermined target flying height by changing a protrusion value by thermal expansion which accompanies electric power distribution to and heating of a heater provided in the head.
2. Description of the Related Arts
Conventionally, the flying height of the head with respect to the recording surface of a magnetic disk has to be reduced in order to realize a high recording density of a magnetic disk apparatus, and a flying height of 10 nm order is realized recently. However, when the flying height of the head is reduced, collision with minute protrusions on the magnetic disk surface is readily generated, and variation of the clearances between heads is present in the range of mechanical common differences; therefore, there is a problem that the flying height cannot be set lower than the range of common differences when the medium contact is taken into consideration. Therefore, recently, like JP2002-037480, there is proposed a method in which variation in the protrusion value (TPR value) caused by a phenomenon in which the head flying surface protrudes toward the direction of the magnetic disk due to temperature increase in a write head (thermal protrusion: TPR) is measured in an examination process or the like and retained in a magnetic disk, and the data is used for controlling flying heights for each head. Furthermore, there have also been proposed methods like JP2005-071546 and JP2005-276284 in which a heater is incorporated in a head, and the clearance between the head and the recording surface of a magnetic disk is controlled by utilizing the protrusion phenomenon caused by thermal expansion of the head flying surface accompanying electric power distribution to the heater. In JP2005-071546, a constant element temperature is maintained by changing the electric power applied to an electricity conduction film provided on the head with respect to increase in the apparatus temperature or the element temperature which is caused by recording/reproduction, thereby maintaining a constant clearance between the element and the recording medium. In JP2005-276284, a flying-height-increasing heating device which increases the distance between the recording/reproduction element and the magnetic disk surface by causing a part of an air bearing surface of the head to expand and protrude by heating, and a flying-height-reducing heating device which reduces the distance between the recording/reproduction element and the magnetic disk surface by causing another part of the head air bearing surface to expand and protrude by heating are provided in the head, and the flying height is corrected such that reproduction can be performed without causing collision during, for example, activation of the apparatus. Moreover, as the method for measuring the changed distance of the flying height between the head of the magnetic disk apparatus and the magnetic disk, a method utilizing the fact that reproduction amplitude lead from Wallace (Wallace) spacing loss is changed in accordance with the flying height is known (U.S. Pat. No. 4,777,544).
However, in such conventional methods of controlling the flying height between the head and the magnetic disk recording surface, basically, the protrusion value is adjusted so that reproduction can be performed without causing medium contact by utilizing the fact that flying height is changed due to expansion/protrusion of the head flying surface when the heater is heated by distributing electric power; and there has been a problem that highly precise flying height control of controlling the flying height upon recording and reproduction to a constant target flying height by taking variation of the flying heights which are different in each head into consideration cannot be performed. Moreover, in the conventional flying height measurement utilizing Wallace spacing loss (Wallace), the flying height is measured from amplitude change in a reproduction signal when the head is caused to fly by activating the magnetic disk apparatus in the state in which the head is in contact with and stopped in a contact-start-stop area of the magnetic disk surface. However, in recent magnetic disk apparatuses, contact-start-stop of the head is abolished, and a head retained in a ramp load mechanism is delivered to the disk surface upon activation of the apparatus in the state in which the magnetic disk is rotating, thereby causing it to fly from the beginning; thus, there is a problem that the amplitude change while the head which is in contact with the magnetic disk surface is flying cannot be detected, and the flying height cannot be measured from unchanged amplitude of the reproduction signal of the head which is flying with a constant flying height.